Heat exchanger



1962 D. J. PEEPS ETAL 3,020,026

HEAT EXCHANGER Filed May '7, 1958 INVENTORS: 1701mm J. PEBPS.

BY HANK 14 H DFFMAN.

AT TY.

United States Patent 3,020,026 HEAT EXCHANGER Donald J. Peeps, Rosstord, and Frank W. Hoffman, Toledo, Ohio, assignors to The De Vilhiss Company, Toledo, Ohio, a corporation of Uhio Filed May 7, 1958, Ser. No. 733,582

. 3 Claims. (257-246) This invention relates generally to a heat exchanger and particularly to one adapted to transfer heat through intervening sheet metal walls from flowing films or ribbons of heat carrying fluid to a ribbon formation of coating material. The heat exchanger of this invention is preferably used in conjunction with a thermostatically controlled heater, with the fluid heating medium traveling between the exchanger and the heater in a low volume, high speed circulating system.

The coating material reaches the heat exchanger from a supply source, ordinarily propelled by air or pump pressure, and continues therefrom to a hose or piping by which it is delivered to a spray gun.

Water makes a very satisfactory low cost heating medium as its fluidity is an aid to fast flow and it is substantially inert chemically in the small quantity involved in such a closed system. Also, the high heat capacity of water facilitates the rapid heat transfer desired.

Material heating equipment of this description has been employed advantageously in many finishing operations involving the spray application of lacquers, synthetic enamels, varnishes and other coating materials. The selected material temperature, usually between 120 and 160 degrees Fahrenheit, reduces the viscosity of the material and thus permits the use of a smaller proportion of thinner, and thinners of lower cost. Because of the resulting heavier body of the material a thicker coating is deposited while the improved flow results in a smoother finish. Numerous related benefits include savings in time and labor, shorter drying periods, fewer rejects, and more uniform quality.

The established design of heat exchanger to which this invention pertains, and which has proved most satisfactory in industrial heating installations, includes four concentric, telescoped tubes sealed at their ends. The three chambers of narrow annular section, formed between the walls of each pair of adjacent tubes, are sealed at their ends except for lateral entry and exit openings. The middle one of the three chambers, constitutes the passage for the coating material to be heated while the inner and outer chambers bordering the inner and outer sides of the material chamber comprise the paths for the heating medium.

To lengthen the heat transfer association of the coating material and the heating medium the material and the medium are directed in helical paths circumferentially around the annular chambers as the material and medium proceed longitudinally of the chambers. These circuitous paths are defined by the courses of a coiled wire secured within eachchamber, the wire having a diameter to substantially span the thickness of the annular section or the chamber.

The employment of light tubes of sheet metal stock reduces the weight of the assembled heat exchanger. Also, such tubes, by possessing a minimum heat storing capacity, eifect a quicker heat transfer and a better control of changes in the heat transfer action. The lightness in weight is further desirable from the standpoint of portability, shipping and basic material costs.

As the need of disassembling a heat exchanger of this design should never arise under ordinary conditions the sealing connections between the tubes may be of a permanent nature. Brazing is the most effective method for joining the tubes together either directly or by separate atcountered in their fabrication.

3,02%,026 Patented Feb. 6, 1962 tachrnent to end caps. Threading would be more expensive and questionable in view of the light guage of the tube stock. Threaded end caps would also have to be of heavier material adding to the total weight and increas ing the heat absorption and dissipation properties of the heat exchanger.

In previous models of this general design of heat exchanger there has been employed a rather ingenious arrangement incorporating end caps of stepped outline fitted over tubes of progressively reduced length from the innermost to the outermost tube. Besides being simple and inexpensive this construction also limited the chance of leaks at the inlet and outlet connections as each of these communicated with the associated chamber by passing through a single thickness of tube Wall.

It is of course most essential that the chambers forming the passageways for the narrow bands of the heating medium and the coating material be definitely and permanently sealed from each other as well as to the atmosphere.

While the performance of heat exchangers of this earlier design has been excellent, some ditticulties have been en- Because of the curved surfaces of the tubes and caps and other variable conditions the brazing action is not always uniform and there are occasional joints that are not completely sealed. As these leakage spots are concealed beneath the end caps their locations are indefinite and no remedial processing has proved feasible. Due to these circumstances the faulty units have had to be scraped. As these constitute an appreciable quantity, quite a monetary loss is involved.

A prime object of this invention is to provide a heat exchanger which may be fabricated easily and in which joints between tubes are exposed and leaks therein easily located and repaired.

An additional object of this invention is the provision of a heat exchanger in which each inlet and outlet connection communicates with a passage of the exchanger through the wall of a single tube.

A further important object is the provisionof a heat exchanger of a simple, sturdy design with a minimum number of parts.

The principal feature through which this invention achieves the above objectives is the shaping of the three inner tubes with an enlarged flared end with each flared end fitting against the end of the next more outwardly positioned tube, and the shaping of the three outer tubes with a reduced end portion with each reduced end portion fitting against the next more inwardly positioned tube.

This arrangement will be described in more detail hereafter and other objects and advantages will be made apparent by the detailed description supplemented by references to the accompanying drawings, in which:

FIGURE 1 is an elevation with parts broken away, of a heat exchanger embodying my invention;

FIGURE 2 is a plan view of the heat exchanger of FIGURE 1;

FIGURE 3 is an elevational view showing how the tubes of the heat exchanger are assembled in telescopic relation; and

FIGURE 4 is an enlarged vertical section of the main body of. the heat exchanger of FIGURE 1.

The heat exchanger pictured in the drawings is normally installed in an upright position as shown. On the lower left side of the main body 6 of the heat exchanger, as viewed in FIGURE 1, there is a pair of inlet connections 8 and 9 for the water, which is preferably utilized for the heating medium. These connections are joined to the small manifold 10 receiving a pump-driven stream of water from an unillustrated heating unit through the supply line 11.

The water entering through connection 8 travels upwardly within the outermost chamber 12 formed between the outside tube 14 and the next inwardly adjacent tube 15. Connection 3* delivers the heated water to the innermost chamber 18 formed between the inside tube 19 and the next outwardly adjacent tube 20. The water travelling upwardly within chambers 12 and 18 is directed in helical paths by the coiled wire 21 and 22 respectively lodged within these chambers. The water issues from the top ends of the chambers through outlet connections 23 and 24, and through manifold 25 to the piping 26, by which it is returned to the unshown heating unit and circulating pump.

The coating material to be heated flows through hose or tubing 28 to connection 29 from a supply source which usually is a pressure feed tank under regulated air pressure. The coating material enters the center chamber 32 formed between tubes and and which is in sandwiched relation to the two hot water chambers. The material progresses downwardly in chamber 32 guided in an helical path by the coil of wire 33 and is discharged from the chamber into connection 34. This movement of the material is in counter flow to the enclosing flattened streams of water by which it is quickly and easily heated through the encompassing tubular surfaces.

It has been found that with a per minute flow of only one gallon of water heated to 185 Fahrenheit in the heating unit, coating material passing through the exchanger at the exceptionally high rate of one quart per minute will be heated and maintained at a temperature between 150 F. and 155 F. The latter temperature is approximately that generally recommended for most materials. A much higher heat endangers the desirable qualities of such coating materials. Obviously, with the temperature of the heating medium restricted to 185 F. objectionable overheating of the coating material is not possible. In ordinary practice there would be even less difference between the water and material temperatures.

The swirling action of the coating material through the helical passage not only facilitates its absorption of heat but also inhibits settling of pigment and adhesion of resinous components.

The path of the material from connection 34 includes tubing 35 and the T manifold 36 which houses a temperature reactive element reporting to the gauge 37. From manifold 36 the material travels through piping 39 and a suitable hose to a spray device.

The flow of coating material is ordinarily intermittent due to the temporary discontinuance of the spray operation while a completely coated product is replaced with the next product to be coated, or while a product is rotated to bring another surface into coating range. The resulting cessations in the coating material flow does not result in overheating of the material in the heat exchanger due to the restraint of the temperature of the water to not more than 185 F.

If the interruptions are sufficiently long to reduce to an undesirable extent the temperature of the static coating material in the hose line to the spray gun, a jacketed hose may be used with passages in its walls through which heated water is circulated.

As may be observed more readily in FIGURES 3 and 4 the outside tube 14 has a main cylindrical section 41 continued uniformly to its lower end 42. The upper end of tube 14 has a tapered portion 43 and a short terminal section 44 of cylindrical form. The inner diameter of the terminal section 44 is dimensioned to receive with a close fit the main cylindrical body 46 of the next, inwardly adjacent tube 15.

Tube 15 at its lower end has an outwardly flaring section 48 and an elongated, cylindrical terminal sleeve 49. The initial portion of sleeve 49 fits snugly against the interior wall of the lower end 42 of outside tube 14 and the end portion of the sleeve extends exteriorly of the end of tube 14.

The upper end of tube 15 has an inwardly tapered section 51 and a final cylindrical end portion 52 projecting from the upper end of tube 14. The cylindrical portion 52 fits closely around the main cylindrical section 54 of the third inwardly placed tube 20. This tube in turn flares outwardly at 56 adjacent to its enlarged lower cylindricai end 57.

The first portion of the cylindrical end 57 of tube 20 nests tightly within the cylindrical end portion 49 of the second outside tube 15 and the balance of the end 57 projects exteriorly of tube 15.

The upper end of tube 20 has an inwardly tapered shoulder 6t and a final short cylindrical collar 61. This cylindrical collar 61 closely embraces the upper end 64 of the inside tube 19. This end of tube 19 is a straight cylindrical extension of its main body portion 65.

The lower portion of the inside tube 19 has a flaring skirt portion 66 merging into a short enlarged cylindrical tip 67. The latter fits within the freely extending final portion of the cylindrical terminus 57 of the tube 20 which is outwardly adjacent to tube 19.

As may be noted by reference to the showing of FIG- URE 4 the inlet 8 and outlet 23 of the outermost water chamber 12 go through only the wall of tube 14 to reach this chamber. Also, inlet connection 29 and outlet connection 34 communicating with the center coating material chamber 32 join the chamber through the single walls respectively of the main cylindrical body 46 and the lower cylindrical end 49 of tube 15. Similarly, inlet 9 and outlet 24 reach directly into the innermost water chamber 18 through the wall of the lower cylindrical terminus 57 and the wall of the upper end of the main cylindrical body 54 of tube 20.

The unique shapes and the combination of concentric tubes of which this heat exchanger is constructed are of special advantage in the fabricating and assembly operations as well as in the form of the final product.

The material for the tubes may be of various thicknesses and composition. However, it is recommended that welded tubing of mild carbon steel with a wall thickness of thirty five thousandths be utilized for the exchanger of the dimensions herein described. A heavier gauge of tubing would ordinarily be employed in larger models and seamless tubing in some cases could be used to better advantage than the welded type. 'Ihe tube lengths for the embodiment selected here for disclosure may range from thirteen inches for the outside tube to nineteen inches for the inside tube. The diameters of the main sections of the tubes may run from one and one eighth inches in increments of one quarter of an inch, to one and seven eighths.

Most of the bell enlargements and reduced collars on the ends of the tubes may be easily and accurately shaped by conventional spinning methods. This fabricating procedure is well adapted to give the rounded corners which case the assembling of the tubes and which present smoother inner passages. Simple expandable forms, however, are preferred for shaping some of the tube ends.

The wire coils creating the edge walls of the helical passages of flat ribbon form are of music wire composition and in one embodiment of the invention are of twenty six gauge which denotes a diameter of sixty three thousandths of an inch. The turns of the wire coils are preferably spaced about one and one half inches apart and the inner diameter of the formed coil is selected to fit tightly over the tube to which is secured by spot weldmg.

The annular channels of the chambers between the tubes should have a width not greatly in excess of the diameter of the wire stock. With wire of the cited twenty six gauge (.063 inch) the recommended thickness of the annular passages would be about nine hundredths of an inch. This combination permits easy asembly of the tubes with the Wire coils in place wound around the outside of the tubes. At the same time the courses of the coils block a suflicient portion of the cross area of the annular passage to function effectively in directing the film of water or coating material in circumferential paths longitudinally of the tubes.

It may be visualized by reference to FIGURE 3 of the drawings how essential for assembly are the enlarged ends of the three innermost tubes and the reduced ends of the three outermost tubes. With the Wire coils fixed to the tubes each tube may be introduced within another tube only through the enlarged end hereof and only by having the entering end of the inserted tube of no greater size than the main cylindrical portion thereof. At the same time the three outer tubes must have the reduced end cylindrical collars to receive and fit around the main cylindrical portions of the tubes over which they are located.

The enlarged cylindrical sections at the flared ends of the two center uoes must also be long enough to overlap the like ends of the adjacent inner tubes, to be overlapped in turn by the next outer tubes, and still have sutlicient area remaining between the lapped and lapping portions for entry or exit connections.

The various tubes and connections are permanently attached together by copper brazing of the joints. This is accomplished by running the units through a brazing oven while horizontally positioned and with a small quantity of the brazing material initially deposited on the top of the crack of each joint. Under the oven heat the copper melts and flows around the seams and by capillary action back under the edge of the overlapping tube ends. Under subsequent tests any leaks are easily located in the exteriorly exposed joints; and then may be remedied by a second brazing operation.

The combined features which the novel arrangement of this invention makes possible include the exposed joints between the water and material chambers, as well as between the inlet and outlet connections and the walls of the chambers with which they communicate; the single walls through which the connections penetrate; the lateral positioning of the connections; the assembly of the tubes with the coiled wires attached thereto; and an overall simple design requiring a minimum number of parts and which is easily and quickly produced with a lower percentage of units discarded because of imperfections.

While heating is the principal function of the subject invention it may of course be used for cooling as well, and the claims should be read to cover such a reverse transfer of heat.

Also, while water and coating material are specifically referred to, such terms should be interpreted sufiiciently broadly to encompass other fluent materials capable of carrying and transferring heat through the disclosed exchanger.

The heat transfer media which may advantageously be substituted for water under some circumstances include soluble oils, transformer oils, and mixtures of glycol, polyglycols and water. The latter combination is suitable for use in portable units subject to freezing temperatures Transformer oils are efiicient due to their freedom from injurious chemicals, their low viscosity, and high heat transfer property. They further aid the functioning of the equipment by being a lubricant for the pump.

Although a specific embodiment has been shown and described it should be taken as an example only and it should be understood that variations of the design may be easily produced without departing from the spirit of the invention. For instance, a more compact and simpler unit could be created by eliminating one of the chambers and employing a water stream on one side only of the coating material passage. Likewise short strips of square as well as round section pieces could be utilized to direct the streams circumferentially in place of the long wire coils disclosed.

It is intended to cover such modifications containing the essence of the invention in the following claims.

We claim:

1. A heat exchanger having telescoped, concentric tubes, spaced from each other to define elongated passages of annular cross section for heat exchange fluids, inwardly tapered. portions of the tubes closing all of said passages at one end thereof outwardly flaring portions of the tubes closing all of said passages at the other end thereof, main cylindrical bodies of the tubes disposed between the tapered and flaring portions thereof, the tubes having cylindrical terminating sections beyond the tapered and flaring portions, each of said terminating sections closely engaging an adjacent tube, the tubes constituting the outer walls of said passages being outwardly and progressively of shorter length and so arranged that each end of each of the said tubes is externally exposed, and inlet and outlet connections for said passages communicating therewith through said exteriorly exposed ends of the tubes.

2. A heat exchanger according to claim 1 in which the exteriorly exposed end of each tube adjacent the tapered portion includes a part of the main cylindrical body of the tube as well as the tapered portion and the cylindrical terminating section thereof.

3. A heat exchanger according to claim 1 in which there is a coiled wire within each passage to cause the heat exchanging fluid to follow a helical path therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 1,005,442 Lovekin Oct. 10, 1911 1,573,223 Coen Feb. 16, 1926 2,499,384 Holm et a1 Mar. 7, 1950 2,762,652 Carter Sept. 11, 1956 2,847,193 Carter Aug. 12, 1958 FOREIGN PATENTS 232,007 Germany Mar. 7, 1911 407,577 Great Britain Mar. 22, 1934 

